Transformer



Sept. 29, 1942. G. CAMILLI TRANSFORMER Filed Aug. 2, 1939 VIII/252191Inventors: Guglielmo Camilii M TJMZM Their Attorney.

Patented Sept. 29, 1942 TRANSFORMER Guglielmo Camilli,-Pittsfleld,Mass., assignor to General Electric Company, a corporation 01 New YorkApplication August 2, 1939, Serial No. 288,000

11 Claims.

The invention relates to electric apparatus, such as transformers andalthough not limited thereto it finds eflicient application to currenttransformers. The primary or high voltagewinding of a currenttransformer is connected in series, with an electrical circuit which mayoperate at a very 'liigh voltage so that the voltage of this winding maybe very high above ground although the voltagebetween the differentparts of the winding and between its terminals is usually verylow.

Very little insulation is therefore necessary be tween diiTerent-partsof the winding but considerable insulation is necessary between thewinding and ground and between the winding and the low voltage orsecondary winding and the magnetic core. Liquid insulation, such as asuitable mineral oil, has been found to be very satisfactory forinsulating high voltage electrical windings but there is sometimes thepossibility of leakage and any large quantity of inflammable oil maycause trouble if it escapes and becomes ignited.

The general object of the invention is to pro- 'vlde an improved currenttransformer construction in which the high voltage winding is immersedin an insulating liquid 50 that no airpockets are present in thewinding, the construction being such, however, that an extremely smallquantity of liquid is necessary.

Another object of the invention is to provide an improved currenttransformer construction which is very compact and inexpensive. Afurther object of my invention is to provide an electric apparatus withan improved winding structure.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing in which Fig. 1 is aview partly in section of a current transformer constructed inaccordance with the invention; Fig. 2 is a sectional view on the line 2-2 of Fig. 1; Fig. 3 is a sectional view on the line 3-4 of v Fig.1.

Like reference characters indicate similar parts 4 in the differentfigures oi the drawing.

The transformer shown in the drawing includes a high voltage winding Illformed of parallel strands ll brazed to the high voltage terminals l2and I3. As shown in the drawing, the high voltage winding II is formedof six parallel strands wound four times around one side of the lowvoltage winding It and the core I 5. The separate strands may beindividually insulated with enamel to reduce eddy currents between thestrands. The low voltage winding I4 is connected to low voltageterminals 16.

The high voltage winding 10 is insulated from ground and from the lowvoltage winding I4 and the magnetic core I 5 by an insulating layer orcovering H which is preferably porous, a good material for this purposebeing crepe paper. This porous insulating layer IT is covered by a layer1 l8 of a suitable fluid impervious material, such as a flexiblematerial or adhesive tape to enclose the winding and its insulatingcovering H in a iii liquid-tight or impervious casing. This adhesivelayer It may be covered with an outer layer or covering I9 of somesuitable mechanically strong tape to prevent mechanical inJury to theadhe-- sive layer during assembly. The porous insulating layer H and theouter layers It and it are extended along the terminal leads of thewinding to the terminals I2 and I3 which are formed with longitudinalopenings or passages 20, as indicated in Figs. 1 and 3. The high voltagewinding i0 is thus efiectively sealed except for the openings 20 in theterminals l2 and I3 which communicate with the spaces and intersticesbetween the strands ll of the winding. After the windings i0 and It withtheir terminals and the magnetic core l5 have been assembled, as shownin Fig. 1, they are enclosed in a solid block 2| of molded material,such as concrete. During the molding of the concrete casing 2|, the highvoltage winding ID is protected from any moisture in the concrete by thesealed impervious layer l8 and the low voltage winding l4 and magneticcore l5 may be protected from this moisture .by an asphaltic or othersuitable coating.

After assembly of the transformer, as much air as practicable is pumpedout of the high volt age winding space and the interstices or restrictedpassages between the turns inside its sealed covering I8 and theinsulating covering which encloses and relatively closely fits thewinding, the air being withdrawn through one of the hollow terminals l2and I3 which have openings beneath the insulating cover andcommunicating with the interstices or restricted passages between theturns. Thus, while the enclosing insulating covering which is relativelyclose to or is contiguous with outside surfaces of winding turns therebyrestricts passages through which gaseous impurities may be withdrawn,since the terminal leads have openings beneath the insu= latingcovering, gaseous impurities such as air may be withdrawn from theserestricted passages or interstices through one of the hollow leads.

While under vacuum, this high voltage winding gaseous impurities frominterstices between a winding turns having a layer of insulationrelatively closely fitting and substantially enclosing the winding,through a tube or hollow terminal communicating beneath the insulatinglayer is described and claimed in my copending application S. N.385,263, filed March 26, 1941, and assigned to the same assignee as thispresent invention. The insulating liquid is filled in to a level 22 wellabove the turns of the high voltage winding H but far enough below theupper ends of the terminals 52 and 3 to leave spaces in the openings 26in these terminals for thermal expansion and contraction of the liquidduring operation of the transformer. The outer ends of the terminals l2and iii are sealed by threaded plugs 23 to exclude air, moisture andother matter which might contaminate the insulating liquid and reduceits dielectric strength. The insulating liquid may be introduced intothe high voltage winding space while hot so as to fill more effectivelyall empty spaces and also so as to cure the sealing layer it and theprotective layer l9 and make them more impervious to outside moisture orto the insulating liquid inside them. These outer sealing and protectivelayers l8 and 29 may also be cured by heating them before the moldedcasing 2! is formed. This might reduce the amount of moisture whichwould have to be dried out of the high voltage winding before theinsulating liquid is introduced. Instead of using concrete in the moldedcasing 2 i, any other suitable material maybe used. A mixture of castingresin and sand has given good results but is of course more expensivethan concrete. As will be seen from the drawing, the casing 2! supportsand protects the sealed impervious flexible covering l8 and provides aunitary structure. Furthermore, if the casing 2! should become crackedor damaged the possibility of leakage of the insulating fluid from theinsulation with the consequent entrance of air and moisture thereto isminimized due to the sealed impervious flexible covering, since thisflexible covering will not originally become cracked or damaged.

The invention provides an extremely compact current transformer havingpractically all the advantages of a dry transformer, due to theextremely small quantity of insulating liquid necessary as theimpervious covering which surrounds and may closely fit or follow thecontour of the insulation minimizes the volumetric capacity of the spacecontaining the liquid, but J 1. A transformer including a winding, solidporous insulation surrounding and closely fitting said winding, aterminal connected to the winding, a sealed impervious flexible coveringaround the winding and extending to the terminal, the terminal having anopening therethrough communicating with the winding space in saidcovering, an insulating liquid in said winding space. said sealedimpervious flexible covering surrounding and closely fltting saidinsulation so. as to minimize the volumetric capacity of the spacecontaining said liquid, and a casing surrounding and substantiallyclosely fitting said sealed in pervious flexible coveringfor supportingand pro tecting said covering.

2. A transformer including a solid porous insulation surrounding andclosely fitting said winding, a terminal connected to the'winding, asealed impervious flexible covering around the winding and extending tothe terminal, the terminal having an opening therethrough communicatingwith the winding space in said covering, an insulating liquid in saidwinding space, a removable seal closing the outer end of the terminal,the level of the liquid being below said seal to permit thermalexpansion and contraction of the liquid, said sealed impervious flexiblecovering surrounding and closely fitting said insulation so as tominimize the volumetric capacity of the space containing said liquid,and means surrounding and closely flttingsaid sealed impervious flexiblecovering for supporting and protecting said covering.

3. A transformer including a winding, a terminal connected to thewinding, a porous insulating covering around the winding, a sealedcovering of adhesive tape around the insulating covering and extendingto the terminal, the terminal having an opening therethroughcommunicating with the winding space in said insulating covering, aninsulating liquid in said winding space and porous covering, said sealedcovering of adhesive tape substantially following the contour of saidinsulating covering so as to the amount of liquid necessary-tosubstantially fill the winding space, and a protective coveringsurrounding and substantially following the contour of said sealedcovering.

4. A transformer including a terminals connected to the winding, aporous insulating covering around the winding, a sealed imperviousflexible covering around the winding and extending to the terminals, theterminals having openings therethrough communicating with the Windingspace in said coverings, an insulating liquid in said winding space,said sealed impervious flexible covering surrounding and closely fittingsaid insulating covering so as to minimize the volumetric capacity ofthe space containing said insulating liquid, and a casing surroundingand closely fitting said sealed impervious flexible covering forsupporting said covering.

5. A transformer including a winding, terminals connected to thewinding, a porous insulating covering around the winding, a sealedimpervious flexible covering around the winding and extending to theterminals, the terminals having openings therethrough communicating withthe winding space in said coverings, an insulating liquid in saidwinding space and porous covering, removable seals closing the outerends of the terminals, at least one of the terminals having a spaceabove the liquid level to permit thermal expansion of the liquid duringoperation of the transformer, said sealed impervious flexible coveringsurrounding and closely fitting said porous insulating covering in orderto minimize the volumetric capacity of the space containing saidinsulating liquid, and means surrounding and closely fitting said sealedimpervious flexible covering for supporting said covering.

6. A current transformer including a winding, said winding comprising aplurality of strands, a terminal connected to the winding, a relativelythin covering of solid porous insulation surrounding said winding,a'sealed impervious flexible covering around said winding and extendingto the terminal, the terminal having an opening therethroughcommunicating with the space within said covering and the intersticesbetween the strands of the winding, an insulating liquid in said spaceand said interstices, said sealed impervious flexible coveringsurrounding and closely fltting said insulating covering so as tominimize the volumetric capacity of the space containing said insulatingliquid, and a casing surrounding and closely fitting said sealedimpervious flexible covering for supporting said covering.

7. A current transformer including a relatively high voltage winding,said winding comprising a plurality of strands, terminals connected tothe winding, a porous insulating covering around the winding, a sealedimpervious flexible covering around the first-mentioned covering andextendmg to the terminals, the terminals having openings therethroughcommunicating with the space within said impervious covering and theinterstices between said strands, an insulating liquid in said space,said interstices and said porous covering, said sealed imperviousflexible covering surrounding and substantially following the contour ofsaid insulating covering and extending to the terminals so as tominimize the amount of liquid necessary to substantially flll thewinding space, a low voltage winding linking saiJ covcred high voltagewinding, and a molded casing surrounding and closely fitting saidwindings for supporting said flexible covering and providing a unitarystructure.

8. A transformer including a winding, a terminal lead extending fromsaid winding, solid porous insulation surrounding said winding and lead,an insulating fluid surrounding said winding and lead and penetratingsaid insulation, a protective and enclosing casing surroundin saidwinding, and a sealed impervious flexible covering within said casingand surrounding said insulation so as to minimize the possibility ofleakage of the insulating fluid from the insulation upon damage to saidcasing.

9. A transformer including a winding, solid porous insulation aroundsaid winding, an insulating fluid surrounding said winding andpenetrating said insulation, fluid impervious flexible means surroundingand substantially following the contour of said solid porous insulationso as to substantially limit the amount of fluid necessary to surroundsaid winding and penetrate said insulation, covering means surroundingand substantially supporting said fluid impervious means for protectingsaid fluid impervious'means from in- Jury or damage, and passage meansextending through said fluid impervious means and said covering meansand communicating with the winding space through which said fluid may beintroduced.

10. A transformer including a winding, solid porous insulation aroundsaid winding, an insulating fluid surrounding saidwinding andpenetrating said insulation, a substantially fluid tight enclosingcasing surrounding said winding and insulation, fluid imperviousflexible means within said enclosing casing and surrounding andsubstantially following the contour of said solid porous insulation soas to substantially limit the amount of fluid necessary to surround saidwinding and penetrate said insulation and for minimizing the possibilityof leakage of the insulating fluid from the insulation upon damage tosaid enclosing casing, and passage means extending through saidenclosing casing and said fluid impervious means and communicaitng withthe winding space through which said fluid may be introduced.

11. In an electric apparatus, a winding having a plurality of turns, aporous insulating covering substantially enclosing and relativelyclosely flt ting said winding, a molded casing surrounding andrelatively closely fitting said winding and insulating covering, and apair of conducting terminal leads connected to said winding, each ofsaid terminal leads having a fluid passage adapted to communicateoutside said insulating covering and having an opening beneath saidinsulating covering and communicating :with the interstices between saidwinding turns so that gaseous impurities may be withdrawn from theinterstices through one of said terminal leads as an insulating fluid isintroduced through the passage of the other of the terminal leads, theinsulating fluid permeating said insulating covering and fllling aportion of each of said fluid passages of i said terminal leads.

GUGLIELMO CAMILLI.

